Five Latvian construction firms on Saturday said their work was not to blame for the roof collapse of a supermarket in Riga, in which at leat 53 people have been killed, dpa reported. The construction activity on the roof at the time of its collapse was in keeping with Latvian regulations and were supervised, the firms said in a joint statement. They announced a "thorough investigation of all possible causes of the collapse of the roof" would be conducted by a team of independent experts. According to the firms, an inspection of the building including the roof was last carried out on November 19, two days before the collapse. "No violations" were found in the inspection, the firms said in their statement.